There is an urgent need for new blood biomarkers for epithelial ovarian cancer (EOC), which is the most lethal gynecological cancer in the United States. CA125 is the most commonly used FDA approved biomarker for EOC, but it is not approved for early diagnosis due to inadequate sensitivity and specificity. Furthermore, although CA125 is commonly used to assist in clinical management of the disease after diagnosis, it cannot be used for the substantial portion of EOC patients where CA125 is not substantially elevated at time of diagnosis, which includes the clear cell and mucinous subtypes. Our long-term goal is to identify novel EOC blood-based and tumor tissue biomarkers and conduct laboratory-scale validation to determine which biomarkers can improve early diagnosis and/or clinical management of this disease. Our overall working hypothesis is that the most specific EOC blood biomarkers will be proteins shed by the ovarian tumor into the blood and that are at very low abundance levels in the blood of cancer-free individuals. During the past grant year, we achieved all goals of the original proposal. Specifically, we identified 29 low-abundance, novel biomarkers using a novel in-depth proteome analysis method to identify human proteins in serum or plasma of xenografted mice containing human tumors. These proteins were then shown to be elevated in blood from EOC patients compared with non-cancer controls using a label-free multiplexed multiple reaction monitoring (MRM) mass spectrometry (MS) assay. We have now narrowed this list to 12 high priority biomarkers using biological and functional criteria Our specific goal for the next grant period is to conduct laboratory-scale validation of these 12 biomarkers in several larger patient cohorts to identify the best biomarkers for early diagnosis of EOC and for improved clinical management of this disease. We will also conduct preliminary evaluations of the capacities of these biomarkers to distinguish among major EOC subtypes, as these are genetically different diseases. To determine whether some biomarkers could complement CA125, we will conduct a focused evaluation of secretomes of clear cell and mucinous ovarian tumors. We will also separately evaluate the predictive value of our biomarkers in the subset of patient plasma samples that exhibit low CA125 levels in our new larger patient cohorts. The two aims that will be pursued over a 5- year period are: 1) Develop tissue and high-throughput preclinical plasma assays for our 12 novel EOC biomarkers, and 2) Validate sensitivity and specificity of our 12 novel EOC biomarker levels in plasma or serum from multiple independent patient cohorts. The biomarkers will be quantified in patient and control plasma or serum using a novel ImmunoMRM method that multiplexes pull-down of targeted intact proteins by commercially-available antibodies using stable isotope-labeled intact proteins as internal standards. It is expected that the subset of our 12 biomarkers that are shown to be useful for early diagnosis and/or clinical management of EOC will advance to larger-scale multi-center, preclinical testing in CLIA certified laboratories in the future.